1. Field of the Invention
The present invention relates to ignition systems for internal combustion engines and, more particularly, to a novel intake, exhaust and torch ignition apparatus for a combustion chamber of a cylinder of an internal combustion engine.
2. The Prior Art
Historically, internal combustion engines incorporate either a compression ignition system (diesel-type), a spark ignition system or variations of these systems to ignite the fuel/air mixture in the combustion chamber. The spark-ignition engine utilizes carburetion (a premixing of the fuel, usually gasoline, with air) prior to directing the fuel/air mixture into the combustion chamber. The conventional carburetor is a relatively inefficient device in that much of the gasoline is not completely vaporized but remains in droplet form as it enters the combustion chamber with the result that some of these droplets are discharged into the exhaust as unburned hydrocarbons. Additionally, the combustion temperature from the spark-initiated ignition is relatively low with the result that there is incomplete combustion so that additional quantities of gasoline are discharged into the atmosphere as unburned or incompletely burned hydrocarbons and carbon monoxide. While strenuous efforts have been directed toward the reduction of these pollutants by various devices including the injection of supplemental air into the exhaust system to continue the combustion process, catalytic convertors, and the like, only modest results have been obtained in spite of the high cost of the apparatus.
Attempts to increase the efficiency of the internal combustion engine and also the horsepower available have succeeded dramatically by using higher compression ratios on the order of about 10:1 or even 11:1. However, gasoline frequently detonates spontaneously at these higher compression ratios with an adverse effect on engine performance and life. The addition to gasoline of detonation inhibitors such as tetraethyl lead, tricresolphosphate, and the like, inhibits detonation thereby accommodating high compression ratios. However, since lead is a significant pollutant, numerous governmental regulations have been adopted against its usage. Accordingly, the current gasoline or spark-initiated engines are directed toward using unleaded gasoline with the result that they cannot be operated at compression ratios much greater than about 9:1 without fear of detonation.
In summary, the current spark-initiated, internal combustion engines have a relatively low efficiency for the following reasons:
(1) Lower compression ratios,
(2) Poor combustion as a result of lower compression ratios and consequent low maximum operating temperature,
(3) Poor combustion as a result of poor carburetion, and
(4) Governmentally-mandated anti-pollution devices which have uniformly reduced engine efficiency.
The compression ignition or diesel-type engine is inherently more efficient than the spark-initiated ignition engine since (1) there is more energy per weight in diesel fuel than gasoline and (2) the engine operates at a higher combustion temperature and compression ratio. Customarily, the compression ratio for a relatively small engine, such as in an automobile, is as high as 23:1 in order for the temperature to be high enough to ignite the injected fuel. The higher combustion temperatures also mean a more thorough combustion of the hydrocarbons and carbon monoxide with a corresponding increased energy release and consequent greater mechanical energy produced for the same volume of fuel consumed. Admittedly, compression-ignition engines characteristically exhibit a lower horsepower per pound of fuel consumed than spark-ignition engines. This lower horsepower generally results from the high peak pressures (which, in turn, require a heavier engine structure) and from other problems which exceed the savings realized from the more thorough combustion.
Ignition in a compression-ignition engine results when an air induction charge is compressed in the combustion chamber to a relatively high pressure and a correspondingly high temperature above the ignition temperature of the fuel so that subsequently injected fuel ignites as it is injected. The fuel must be injected rapidly, or almost all at once, so that there will be at least some of the injected fuel that is an appropriate mixture of fuel and air for immediate autoignition. However, other parts of the injected mixture will be typically too rich for ignition while some parts will be too lean, although injection almost all at once insures that at least some of the fuel and air will be at the appropriate mixture for instantaneous ignition.
On the other hand, if the fuel is injected slowly, ignition will not start instantaneously because there will not always be a correct mixture for ignition at the instant of injection. After enough fuel has finally been injected so that some of it is at the correct mixture, it will ignite. However, by the time ignition occurs, a considerable quantity of fuel that had previously been injected will be relatively close to the correct ignition mixture so that it will ignite from the mixture that actually was first ignited, although later injected. Upon this occurance, the large quantity of previously injected fuel ignites extremely rapidly with a consequent very rapid and abnormally high rise in the cylinder pressure and temperature. This phenomena is essentially equivalent to a secondary detonation of "carbureted fuel." This is not desirable and can result in piston and cylinder damage. As a result, a small to medium-size, diesel-fueled, compression-ignition engine requires that all of the fuel that is supplied to a cylinder in a particular stroke or revolution must be injected at once in order to prevent the subsequent detonation caused by the combination of (a) carburetion and (b) delayed ignition that occurs when the fuel is injected slowly.
Although it is necessary for a rapid and full injection of fuel to prevent abnormal and unwanted detonation of "carbureted fuel", this very process causes most of the problems in small automobile-sized diesel engines. When all of the fuel is injected, the subsequent pressure and temperature rise is virtually uncontrolled and both rise to very high values early in the power part of the stroke. This pressure rise is so rapid that the peak pressure occurs before the sine of the power angle is large enough to produce very much torque. For example, at top dead center (TDC) with the power angle at 0 degrees, any amount of pressure would produce zero torque since the sine of 0 degree is zero. Furthermore, if the peak pressure occurs at a power angle of about 10 or 15 degrees, the sine of the angle is still modestly low so that not much torque results. However, the structure of the engine must be sufficiently strong so as to be able to withstand these relatively high pressures. Engine strength is usually defined by engine weight so that the resulting heavy piston and connecting rod parts restrict the maximum speed of the engine and make it relatively sluggish so that it cannot increase in speed rapidly or operate very fast.
A second problem arises from the requirement that the diesel fuel be injected all at once. When autoignition occurs and thus initiates the overall combustion process in the cylinder, secondary turbulence produced by the initial combustion causes the remainder of the fuel to mix with air in the cylinder so that the combustion process can continue. However, this process is not very efficient and much of the fuel is never suitably mixed with air. The unmixed fuel is turned to carbon particles by the high temperatures and is discharged into the exhaust as soot. Exhaust soot is the primary pollutant in a small diesel engine, and it also infiltrates into the oil system necessitating relatively frequent oil changes. Although carburetion would be an excellent solution to the soot problem of the diesel engine so that essentially all of the fuel could be burned, the very fact that carbureted diesel fuel burns so rapidly--approaching or encompassing detonation speeds and pressures with attendant problems described above--makes full carburetion an almost impossible, idealistic goal.
A third problem arises from the high temperature that results from having to inject all of the fuel at once. The high temperatures that occur in a diesel engine are so high that a large percentage of the nitrogen combines with oxygen and is discharged into the air as oxides of nitrogen.
As noted before, combustion pressure is almost completely uncontrollable in spark and compression ignition engines. About all that can be controlled in these engines is the maximum pressure. Subsequent power angle pressures largely follow the formula PV/T=C, and are definitely not optimum for maximizing efficiency and horsepower while minimizing pollutants.
While the fuel-air charge in most spark ignition engines at the time of combustion is essentially a homogenous and vaporized mixture of fuel and air; if the distribution of fuel is not uniform within the chamber, zones of varying air/fuel ratios will be present. Such a mixture is termed a stratified charge. For example, in a stratified charge, the air/fuel ratio at one point in the chamber might be 16:1 while only air might exist at another point in the chamber. The purposes of the stratified charge, spark ignition engine are to: (1) permit use of a leaner mixture than could ordinarily be used in producing ignition successfully; and (2) avoid knock with the result that either high compression ratios or low-grade fuels (or both) can be used. A stratified charge can theoretically eliminate knock because the end gas need not be a combustible mixture. The residence (heating time) of the fuel is also short because injection begins late in the compression stroke.
The stratified-charge principle is one technique used for obtaining high compression (expansion) ratios in combination with spark ignition. However, it is difficult to initate combustion in lean mixtures by a spark discharge and, since mixtures are never perfectly homogeneous, several regions might necessarily have to be ignited to assure continued flame propogation. Additionally, the propogation of the flame becomes increasingly slower as the ratio of fuel to air is reduced, until it virtually ceases at values of approximately 0.025 (fuel-air ratio). Accordingly, the release of energy arising from, say, two ignition points would be extremely slow. One solution to this problem is offered by the use of a dual-fuel diesel engine. In this engine, a homogenous and lean mixture of gas and air is compressed to a high pressure and temperature and thereafter ignited by injecting a small pilot charge of fuel oil. The small spray of oil establishes a large number of ignition points, not on the edges of the chamber as with sparkplugs, but throughout the entire gas-air mixture. The mixture ratio in the vicinity of the oil droplets will be enriched and combustion will start smoothly and rapidly. A number of flame fronts will thereby be established, although as each flame penetrates into the gas-air mixture, its progress will become slower. In fact, if the air-gas ratio exceeds about 40 to 1, the flame may be extinguished in part, as evidenced by unburned fuel in the exhaust. Therefore, it is interesting to note that in the dual-fuel engine, combustion starts in similar fashion to a compression ignition engine and combustion continues by flame propogation, in a similar fashion to a spark ignition engine. The advantage of a dual-fuel engine is that it will exceed the performance of a straight diesel engine at full load, since vaporized gasoline or gas is present in all parts of the chamber and therefore, more air can be burned.
The principle of one experimental engine can be visualized by assuming a circular motion of the air in the cylinder on the compression stroke. At about 50.degree. before top dead center, let a nozzle start to inject fuel tangentially into the air stream and continue the injection for, say 50.degree. of crank movement (at full load). Meanwhile, in a position downstream from the nozzle, a sparkplug is located, and, after injection begins, a spark occurs (say 30.degree. before TDC) when initial fuel-air mixture is swept by turbulence (air swirl) past the sparkplug. Here the flame will be initiated and propogated, mainly in a direction opposite to the swirl with establishment of a burning zone. The liquid fuel leaving the nozzle will vaporize, mix with air, and then burn, thus establishing the lower boundary of the zone. The products of combustion will be carried out of the burning zone and swept around the combustion chamber. In this manner, the fuel/air mixture will be burned directly after the fuel enters the chamber, and without waiting for a flame to travel to the mixture position in the combustion chamber.
Conventionally, the develoment of an injection-type, stratified-charge engine introduced a new problem of coordinating the injection of fuel with the design and turbulence of the combustion chamber. This coordination has not only been difficult to achieve, but it has been indicated to be rather improbable that one design could successfully operate over wide limits of loads and speeds utilizing the present systems for ignition. In particular, the nozzle must not only give good atomization but also selective distribution: a local combustion area must originate and develop from the spark plug location. Moreover, the nozzle and turbulence must, in some manner, follow the principles dictated by volume distribution, if the pressure rises are to occur at the most advantageous crank angles. It has, therefore, been indicated to be quite improbable that the process will give, in itself, such optimum pressure-like characteristics. The primary advantage to the injection-type, spark ignition engine is that it can handle a number of fuels (fuel oil or gasoline) while other engines are more particular since knock, a destructive process, can intervene.
A third type of engine is the torch-ignition engine. It utilizes neither a spark nor high compression to initiate combustion. Ignition is produced at the proper part of the stroke by extremely hot gases in the form of a torch or searing flame. Inasmuch as the torch technology is not subject to the inhibiting deficiencies of either the spark or compression-type engines--as will be shown--all of the weaknesses of these other two kinds of engines can either be ameliorated or wholly eliminated, thus increasing efficiency and horsepower while decreasing the presence of pollutants. For example, the optimum compression ratio for a small automobile engine is about 16:1. At this compression ratio, efficiency and horsepower can be maximized and the creation of pollutants can be minimized. While a torch can ignite a fuel at a compression ratio of 16:1, a carbureted gasoline spark-initiated engine will detonate at that ratio and a small compression ignition or diesel-fueled engine would not ignite at all at that ratio unless very hot. Inasmuch as efficiency increases rapidly up to a compression ratio of about 16:1, controlled fuel injection with a torch ignition system can always be operated at the most efficient compression ratio because ignition is always assured and timing of ignition is completely controllable.
Torque, and hence horsepower, can also be maximized at optimum power angles while concurrently limiting extreme maximum pressures and temperatures. This is accomplished by injecting fuel at the optimum angle near TDC, and regulating or controlling the injection rate so as to predetermine the resulting pressure rise from combustion at the desired optimum value for each arc of the power angle--the angle of the crankshaft between TDC and commencement of exhaust.
In summary, each prior art system is directed toward providing an internal combustion engine that is more economical in its consumption of fuel and/or more efficient in the fuel combustion. However, none of the known devices relate to an internal combustion engine apparatus and method whereby a lean fuel/air mixture is contained within the combustion chamber while a flame front is created within the combustion chamber by injecting high temperature gasses and additional fuel into the combustion chamber.
In view of the foregoing, it would be a significant advancement in the art to provide a novel internal combustion engine apparatus and method whereby a flame front is created within the compressed air or lean fuel/air mixture in the combustion chamber of an internal combustion engine, the flame front being created by injecting high temperature gasses and additional fuel into the combustion chamber. It would also be an advancement in the art to provide a novel internal combustion engine apparatus and method whereby the fuel/air mixture is introduced into the combustion chamber in a swirling motion to thereby continuously feed the fuel/air mixture through the flame front during the combustion cycle. It would also be an advancement in the art to provide a novel intake and exhaust apparatus and method thereby readily adapting the apparatus and method of this invention to an internal combustion engine. Such a novel internal combustion engine apparatus and method is disclosed and claimed herein.